A commonly known process comprises the manufacture of styrene and propylene oxide starting from ethylbenzene and propene. In general such process involves the steps of (i) reacting ethylbenzene with oxygen or air to form ethylbenzene hydroperoxide, (ii) reacting the ethylbenzene hydroperoxide thus obtained with propene in the presence of an epoxidation catalyst to yield propylene oxide and 1-phenylethanol, and (iii) converting the 1-phenylethanol into styrene by dehydration using a suitable dehydration catalyst.
As described in U.S. Pat. No. 4,400,558, oxidation of ethylbenzene gives by-products such as 1-phenylethanol and acetophenone, and in minor amounts 2-phenylethanol and its precursors, such as 2-phenylethyl hydroperoxide. In step (ii) ethylbenzene hydroperoxide is itself converted to 1-phenylethanol, while more acetophenone and 2-phenylethanol are formed as by-products. Propene, ethylbenzene and propylene oxide are usually removed from the reaction mixture of step (ii) by distillation. The residue comprises 1-phenylethanol, acetophenone and a variety of by-products including 2-phenylethanol. This residue is subjected to step (iii). Styrene and acetophenone are usually removed from the reaction mixture obtained in step (iii), and the reaction mixture obtained can be recycled and sent again to the dehydration unit. The acetophenone rich fraction is generally hydrogenated to convert acetophenone to 1-phenylethanol, which can also be sent to the dehydration unit.
A problem of 2-phenylethanol is that it is less easily converted into styrene while it cannot easily be separated from 1-phenylethanol by distillation. This means that 2-phenylethanol tends to build up in the dehydration unit.